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temp gauge and radiator temp disagree

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Old 07-13-2018, 06:40 PM
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temp gauge and radiator temp disagree

so I am running a holley HP efi setup and I am having some cooling issues. It is a highly custom 383 with a procharger. Car is running original v8 radiator and tpi dual fans.

now the car sat in my garage for about 10 years and now money/time/interest have got me back into it. the temp gauge in the cluster and the direct CTS readout on my laptop both agree the engine coolant temp just keeps running north. I'm not talking about high throttle driving, just 25mph in my subdivision. The factory radiatior should be capable of dealing with that as the engine is only make a hundred some horsepower (if that) in that situation. What I find interesting is I put a temp gauge radiator cap on and when the CTS is reading 220, the rad gauge only reads 200. Is this a flow issue? The upper rad hose is hot and clearly flowing as its firm. Just wondering if the issue I am seeing is a function of limited flow. The cap gauge seems to be accurate with room temp when the car is cold.

Thought?
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Old 07-13-2018, 08:32 PM
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Re: temp gauge and radiator temp disagree

Did all the readings agree 10 years ago? Is this with 10 year old coolant?
A lot can happen while sitting for 10 years. Dead coolant, electrolysis, & corrosion come to mind.
Give it a good flush and replace the coolant for starters.
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Old 07-13-2018, 11:34 PM
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Re: temp gauge and radiator temp disagree

In my car, the gauge will read 260, while the ECM is telling TunerPro the temp is 170.

A laser temp gauge on the upper radiator hose reads 210.
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Old 07-14-2018, 12:49 PM
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Re: temp gauge and radiator temp disagree

The radiator was drained and refilled during the rebuild, but it was never "flushed". Coolant did sit in the system for 10 years. The temp gauge and the lap top agree on readout which makes me believe the engine is continuing to heat. I will try and flush it this week to see if it at least makes them agree.
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Old 07-14-2018, 01:33 PM
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Re: temp gauge and radiator temp disagree

My factory gauge read ~270 when my factory fan kicked on at 235. I verified 235 with an IR gun and aftermarket gauge. Now I have a 212F fan switch the factory gauge reads about 230 when that comes on where aftermarket is 210.
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Old 07-14-2018, 07:40 PM
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Re: temp gauge and radiator temp disagree

Originally Posted by 1992rs/ss View Post
The radiator was drained and refilled during the rebuild, but it was never "flushed". Coolant did sit in the system for 10 years. The temp gauge and the lap top agree on readout which makes me believe the engine is continuing to heat. I will try and flush it this week to see if it at least makes them agree.
An old school radiator shop told me years ago to use Lestoil and water to flush, and do a flush with baking soda to neutralize any acids. Do it as many times as needed to come clean. It is summer now, so you can drive around for a couple of days with the Lestoil and then rinse without fear of freezing temperatures and cracking the engine block. When you are finally ready for the new coolant, USE DISTILLED WATER. Usually costs less than $1.00/gallon. You should drain the block also - it's the plugs down low on each side of the engine block, just above the oil pan rail. The knock sensor is usually screwed in at one of them. Sometimes those plugs can be stubborn to get out.
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Old 07-17-2018, 08:40 PM
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Re: temp gauge and radiator temp disagree

could also be were u mounted the sensors as to the different temps
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Old 07-20-2018, 10:07 PM
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Re: temp gauge and radiator temp disagree

Any time you up horsepower and compression ratio, you also need to update the whole cooling system. Doesn't matter slow cruise speed and RPM's.
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Old 07-25-2018, 03:40 PM
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Re: temp gauge and radiator temp disagree

Not clear from the thread what is really the problem. As you're driving around the neighbor hood, the temp is escalating, which is normal to a point. Does it ever reach a stable value? If so, what, as measure by trusted devices, like the laser temp gauge on the radiator core, or the rad cap gauge. I would use these as starting point to determine other issues, like sensors generating correct output. If the system is adequately clean, the stock v8 radiator may not be enough capacity under higher load conditions, like highway cruising, & or external ambient temperature, etc..

Hope this helps, keep us posted.
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